pipeline.hifa.cli.hifa_diffgaincal

hifa_diffgaincal(vis=None, flagging_frac_limit=None, hm_spwmapmode=None, missing_scans_frac_limit=None) → ResultsList[DiffGaincalResults][source]

Derive SpW phase offsets from differential gain calibrator.

This task creates the spectral window phase offset table used to allow calibrating the "on-source" spectral setup with phase gains from a "reference" spectral setup. Currently this setup with two different SpectralSpecs is used by the band-to-band mode, for a high and low frequency band.

A bright point source quasar, called the Differential Gain Calibrator (DIFFGAIN) source, is used for this purpose. This DIFFGAIN source is typically observed in groups of interleaved "reference" and "on-source" scans. These blocks typically occur once at the start and once at the end of the observation. In very long observations, there may be a group of scans occurring during the middle.

The procedure for the phase calibration process is as follow:

  • reference calibration uses the "reference" spectral setup, the "low" frequency for band-to-band observations. The solint is fixed as 'inf' (i.e. solutions are made per scan). Spectral window combination is governed by the hm_spwmapmode options described below. In standard pipeline operation auto is used - basing spw combination upon SNR and flagging level. These reference phase solutions are later applied on-the-fly while solving the (band-to-band) phase offset. The premise being that the reference solutions correct for atmospheric phase variability.

  • phase offset (i.e. the band-to-band correction) calibration uses the "on-source" spectral setup, the "high" frequency for band-to-band observations. The above reference phase corrections are applied on-the-fly using a linearPD interpolation - this corrects (scales) the phases according to the different ratio of the frequency bands. The solint = 'inf' and each group of scan blocks (typically at the start and end of the observation) are combined respectively. The phase offset solution generally comprises of 2 time solutions per spw, per polarization. Spectral window combination is governed by the hm_spwmapmode options described below. auto is used - basing spw combination upon SNR and flag data. These solutions are stored in the pipeline context for later application to the TARGET and CHECK intent(s).

  • residual offset solutions are produced by applying both reference and band-to-band phase offset solutions to the 'on-source' DIFFGAIN intent on-the-fly, and subsequently solving phases per spw, per scan using solint='inf'. Spectral window combination is governed by the hm_spwmapmode options described below. auto is used - basing spw combination upon SNR and flagging level.

Parameters:

  • vis --

    The list of input MeasurementSets. Defaults to the list of MeasurementSets specified in the pipeline context.

    Example: ['M32A.ms', 'M32B.ms']

  • flagging_frac_limit -- if the fraction of flagged data in the temporary phase gaintable exceeds this limit then SpW combination is triggered.

  • hm_spwmapmode --

    The spectral window mapping heuristic mode. The options are:

    • 'all': SpW combination is forced for the diffgain

      low-frequency reference intent solutions, the diffgain high-frequency source intent solutions (actual band-to-band offsets), and for the diagnostic residual phase offsets on the diffgain high-frequency source intent.

    • 'auto': Assess need for SpW combination based on SpwMapping

      from hifa_spwphaseup, and where necessary check the gaintable for missing SpWs / too many flagged data / too few scan solutions.

    • 'both': SpW combination is forced for the diffgain

      low-frequency reference intent solutions and for the diagnostic residual phase offsets on the diffgain high-frequency source intent.

    • 'offset': SpW combination is forced for the diffgain

      high-frequency source intent solutions (actual band-to-band offsets).

    • 'reference': SpW combination is forced for the diffgain

      low-frequency reference intent solutions.

    • 'residual': SpW combination is forced for the diagnostic

      residual phase offsets on the diffgain high-frequency source intent.

    Example: hm_spwmapmode='auto'

  • missing_scans_frac_limit -- if the fraction of missing scans in the temporary phase gaintable exceeds this limit then SpW combination is triggered.

Returns:

The results object for the pipeline task is returned.

Examples

  1. Derive SpW phase offsets from differential gain calibrator.

>>> hifa_diffgaincal()